In the field of LED drivers for offline applications such as retrofit lamps, solutions are demanded to cope with high efficiency, high power density, long lifetime, high power factor and low cost, among other relevant features. While practically all existing solutions compromise one or the other requirement, it is essential that the proposed driver circuits properly condition the form of the mains energy to the form required by the LEDs, while keeping compliance with present and future power mains regulations. It is of critical importance to guarantee a maximum perceptible light flicker at the same time that the power factor is maintained above a certain limit.
WO 2010/027254 A1 discloses a lighting application comprising an LED assembly comprising a serial connection of two or more LED units, each LED unit comprising one or more LEDs, and each LED unit being provided with a controllable switch for substantially short-circuiting the LED unit. The lighting application further comprises a control unit for controlling a drive unit and arranged to receive a signal representing a voltage level of the supply voltage, and control the switches in accordance with the signal. Further, there is provided an LED driver that enables operating a TRIAC-based dimmer at an optimal holding current and an LED driver comprising a switchable buffer, e.g. a capacitor.